On the earthly plane you can see a father-carpenter who is working in his workshop but in spiritual way the carpenter6) is a symbol of Christ. A harp was Davids instrument and is with its triangular form a symbol of the Trinity. David and Goliath7) are in a spiritual way symbols of good and evil. The two columns, joined with a plank, alludes to "The Joiner" (Christ).
6) In some cathedrals you can see sculptures of Christ as carpenter, for example in La Sagrada Familia in Barcelona, Spain.
7) Fröbel was inspired of a poem, well known in Germany: "Giant Goliath was once alive, A very dangerous man ...".